In recent memory hard disk drives, high storage capacity and miniaturization have been demanded. In order to increase the recording density, it has been urged to lower the flying height of a magnetic head and to reduce the unit recording area. Along with this trend, the surface qualities required after polishing have become severely assessed every year even in a manufacturing step for a substrate for a magnetic disk. In order to satisfy the lowering of flying height of the magnetic head, the surface roughness, the microwaviness, the roll-off and projections are required to be reduced, and in order to satisfy the reduction in unit recording area, the acceptable number of scratches per one side of the substrate has been reduced, and the sizes and depths of the scratches have become increasingly smaller.
Also, in the field of semiconductors, highly integrated circuits and higher speed at the operating frequencies have been advanced, and the production of thinner wiring is required especially in highly integrated circuits. As a result, in the method for manufacturing a substrate for semiconductors, since the focal depth becomes more shallow with the increase in resolution required for an exposure device during the exposure of a photoresist, even more improvement in surface smoothness and planarization is desired.
On the other hand, improvement in the production efficiency of the substrate has been increasingly required over the years, so that a substrate having excellent surface smoothness and being capable of being polished in a short period of time has been desired.
In order to meet such requirements, a polishing composition capable of improving surface smoothness of a substrate by using a colloidal silica prepared in accordance with an alkoxysilane method as an abrasive is disclosed in JP-2001-269857 A. However, the improvement cannot be said to be satisfactory for a substrate for high recording density.